Riverine evidence for the significant anthropogenic impact on sulfur and carbon biogeochemical cycle: A case study...

Anthropogenic emissions of sulfur are significantly impacting the biogeochemical cycles of sulfur and carbon at the catchment scale through various chemical processes. However, research on the continuous decadal-scale observations on riverine sulfate flux and its sources, remains limited. In this study, we compiled a river chemistry dataset for the lower reaches of the Xijiang River from 1985 to 2015 and utilized a Monte Carlo inversion model to partition the sources of dissolved loads. Results show that riverine sulfate concentrations in the Xijiang River have more than tripled over the studied 30-year period, with the sulfate yield increasing more than twofold, from 4.36 × 10⁴ mol km^-2 yr^-1 in 1985 to 15.00 × 10⁴ mol km^-2 yr^-1 in 2015. The rapid rise in sulfate yield is largely driven by increased contributions from acid rain (deposition) and pyrite oxidation. Additionally, CO₂ yield through the reaction between sulfuric acid and carbonates in the Xijiang River Basin has accelerated, offsetting CO₂ sequestration by silicate weathering since the 2000s. Our findings underscore the rapid and significant impact of human activities on the biogeochemical cycles of sulfur and carbon over decadal timescales.